A Hybrid Automatic Retransmission Request (HARQ) is a mechanism for improving the performance of a wireless communication system. On a downlink of the system, an application process of the HARQ is described as follows: A base station (BS) first sends a data block and control information related to the data block to a certain user; after correctly receiving the control information, the user checks the data block corresponding to the control information. If the check result is correct, an acknowledgement (ACK) is sent to the BS; after receiving the ACK, the BS regards that the data block is received by the corresponding user correctly, so a new data block can be sent to the user. If the check result is incorrect, the user sends a negative acknowledgement (NACK) to the BS; the BS re-transmits the sent data block to the user until the user returns ACK after correctly receiving the data block, or until the maximum re-transmission number is exceeded. In addition, if the user does not correctly receive the control information related to the data block, the user does not detect the data block or return the corresponding ACK or NACK on an uplink, so the user enters a Discontinuous Transmission (DTX) state. The BS knows that the user is in the DTX state through energy detection; at this time, the BS re-sends the data block and the control information.
In a 3rd Generation Partnership Project (3GPP) Long Term Evolution-Advanced (LET-A) Frequency Division Duplex (FDD) system, in order to support a wider system bandwidth, multiple frequency bands are supported simultaneously, which means spectrum aggregation, and data blocks are transmitted in every frequency band. For the data block transmitted in each downlink frequency band, the user needs to return a corresponding ACK or NACK, or enter the DTX state (which is referred to as returning an A/N/DTX in brief). It means that the user needs to return a plurality of A/N/DTXs in the uplink frequency bands. In a 3GPP LTE Time Division Duplex (TDD) system, downlink data is usually transmitted by multiple consecutive sub-frames. Referring to FIG. 13, the BS sends data blocks in multiple downlink sub-frames to a user, and in an uplink sub-frame, the user returns the A/N/DTX for the data block in each downlink sub-frame, which means that a plurality of A/N/DTXs needs to be returned in one sub-frame. In the existing 3GPP LTE TDD system, an A/N bundling method is used, that is to say, only one A/N is obtained after a logical AND operation on the A/N of each downlink sub-frame, and then the A/N is sent in an uplink sub-frame. In the bundling process, the DTX is regarded as a NACK.